What makes the Earth suitable for life?

Credit: ESO/B. Tafreshi (twanight.org)

Life is vulnerable. Too much heat and harmful radiation, or too little water or energy, and our planet’s vibrant biosphere would vanish. Earth is our spaceship, protecting us from the harsh conditions in empty space.

Vital sunlight: The Sun is the source of life. Without the enrgy of our own star, the Earth would be an inhospitable, dark and frozen world
Credit: ESO/B. Tafreshi (twanight.org)
Water power: Even in the driest regions on Earth, like the Chilean Atacama Desert, water provides conditions that are sustainable for life.
Credit: ESO
Habitable world: Energy and water can turn any hostile environment into a lush and fertile paradise, as evidenced by the Paranal Residencia.
Credit: ESO/José Francisco Salgado

No one knows exactly how life began. But we do know how tricky it must have been to sustain. Everything has to be just right: the amount of light and heat from the Sun; the availability of liquid water; protection from ultraviolet radiation and energetic particles; a relatively stable climate; the right chemical and energy balance; and so on. There have been times in the geological past when the Earth was on the verge of turning into a permanently frozen snowball or a superheated furnace, but so far our home planet has remained habitable.

Habitable zone
Comfort zone: Every star has its own habitable zone – the region where a planet’s surface temperature allows for the existence of liquid water (shown here in green). Closer to the star water evaporates and further away it freezes.
Credit: ESO/NASA/N. Bartmann
Artist's impression of solar wind
Shields up: The Earth’s magnetic field shields us from lethal energetic particles in the solar wind. Without this protection, life would not be possible.
Credit: K. Endo

Without the Sun, or the oceans, or the Earth's magnetic field, life would not be possible. We're lucky to live on a hospitable planet.